MAGNETIC CORE FLUX CANCELING OF FERRITES IN MRI

• US 20090204182A1
• Filed: 02/06/2009
• Published: 08/13/2009
• Est. Priority Date: 02/11/2008
• Status: Active Grant

• Current Assignee: Cardiac Pacemakers Incorporated (Boston Scientific Corporation)
• Original Assignee: Cardiac Pacemakers Incorporated (Boston Scientific Corporation)
• Inventors: Ameri, Masoud
• Granted Patent: US 8,311,637 B2
• Time in Patent Office: Days
• US Class Current: 607/63
• CPC Class Codes: A61N 1/3718 Monitoring of or protection against external electromagnetic fields or currents
• CPC Class Codes: A61N 2/002 in combination with another treatment

Abstract

A magnetic core flux canceling device according to embodiments of the present invention includes a magnetic field sensor adapted for placement at a ferrite material core in an implantable medical device, the magnetic field sensor adapted to transmit a signal corresponding to a magnitude of a first magnetic field. Such a device may also include a coil disposed around the ferrite material core and a driver circuit configured to receive the signal and to vary a voltage applied across the coil based on the signal, the voltage applied across the coil creating a second magnetic field at least partially in a direction opposite the first magnetic field. According to some embodiments of the present invention, multiple coils may be used to cancel magnetic fields in multiple directions. A voltage applied across the coil varies in magnitude and/or direction to cancel or weaken an MRI-related magnetic field.

Claims

1. A device comprising:

a magnetic field sensor adapted for placement at a ferrite material core in an implantable medical device, the magnetic field sensor adapted to transmit a signal corresponding to a magnitude of a first magnetic field at the ferrite material core;

a coil disposed around the ferrite material core; and

a driver circuit configured to receive the signal and to vary a voltage applied across the coil based on the signal, the voltage applied across the coil creating a second magnetic field at least partially in a direction opposite the first magnetic field.

2. The device of claim 1, wherein the driver circuit is further configured to vary a polarity of the voltage applied across the coil to create the second magnetic field in one of two opposite directions.

3. The device of claim 1, wherein the coil is a first coil, the device further comprising:

a second coil disposed around the ferrite material core, the second coil capable of generating a third magnetic field at least partially directed orthogonally to the second magnetic field.

4. The device of claim 3, further comprising:

a third coil disposed around the ferrite material core, the third coil capable of creating a fourth magnetic field at least partially directed orthogonally to the first and second magnetic fields.

5. The device of claim 1, wherein the second magnetic field is equal in magnitude to the first magnetic field.

6. The device of claim 1, wherein the second magnetic field is smaller in magnitude than the first magnetic field, and wherein the second magnetic field is large enough to prevent the ferrite material core from entering a saturation state.

7. The device of claim 1, wherein the driver circuit is a comparator.

8. The device of claim 1, wherein the driver circuit is a high gain differential circuit.

9. The device of claim 1, wherein the ferrite core material is a transformer core in the implantable medical device.

10. The device of claim 1, wherein the ferrite core material is an inductor core in the implantable medical device.

11. A device comprising:

a magnetic field sensor adapted for placement near a ferrite material core in an implantable medical device, the magnetic field sensor adapted to transmit a signal corresponding to a magnitude of a first magnetic field near the ferrite material core;

a low pass filter adapted to filter the signal into a filtered signal;

a coil disposed around the ferrite material core; and

a driver circuit configured to receive the filtered signal and to vary a voltage applied across the coil based on the filtered signal, the voltage applied across the coil creating a second magnetic field at least partially in a direction opposite the first magnetic field.

12. The device of claim 11, wherein the driver circuit is a comparator.

13. The device of claim 11, wherein the driver circuit is a high gain differential circuit.

14. The device of claim 11, wherein the ferrite core material is a transformer core in the implantable medical device.

15. The device of claim 11, wherein the low pass filter filters out components of the signal related to normal operation of the transformer core.

16. The device of claim 11, wherein the ferrite core material is an inductor core in the implantable medical device.

17. An implantable medical device comprising:

a magnetic field sensor adapted to sense a direction and a magnitude of a first magnetic field and to transmit a signal indicating the direction and the magnitude;

a ferrite material core;

a coil around the ferrite material core; and

a driver circuit configured to receive the signal and to select a voltage applied across the coil based on the signal, the voltage applied across the coil creating a second magnetic field at least partially in a direction opposite the first magnetic field.

18. The implantable medical device of claim 17, wherein the driver circuit is further configured to vary a polarity of the voltage applied across the coil to create the second magnetic field in one of two opposite directions.

19. The implantable medical device of claim 17, wherein the coil is a first coil, the device further comprising:

a second coil around the ferrite material core, the second coil capable of creating a third magnetic field at least partially directed orthogonally to the second magnetic field.

20. The implantable medical device of claim 19, further comprising:

a third coil around the ferrite material core, the third coil capable of creating a fourth magnetic field at least partially directed orthogonally to the first and second magnetic fields.

21. The implantable medical device of claim 17, wherein the second magnetic field is equal in magnitude to the first magnetic field.

22. The implantable medical device of claim 17, wherein the second magnetic field is smaller in magnitude than the first magnetic field, and wherein the second magnetic field is large enough to prevent the ferrite material core from entering a saturation state.